rough idle, runs rich, no codes, misfire

[NintendoKD]

Ok, just like the title says. I have replaced every piece of emissions control equipment on this thing. I have a rough, low idle "about 700 rpms" although the inductive timing light says otherwise. new plugs and wires, new coilpack, has a misfire on all cyl. like a stutter, as if they are trying to catch up. I completely smoked the intake and found/fixed all vacuum leaks, as well as the exhaust. New cats and o2's. I am stumped and at the end of my rope. I had the computer rebuilt at a place in Jacksonville FL. that specializes in this sort of thing. I can't smog or register this thing until I get it fixed. What do I do and where do I start? NEW: maf, ait, iac, egr, dpfe, o2's, cats, fuel filter, air filter, fuel pump "good fuel pressure now", plugs, wires, coil, pcv, manifold gaskets "upper and lower" exh. mani gaskets, "one side was leaking" any component that was listed here tested bad and was replaced, this was all done at relatively the same time, as the vehicle hasn't/can't be driven because of smog issues. I want to just shoot this damn thing and be done with it. The misfire is soft, and on all cyl, doesn't throw any codes, pending or otherwise. runs rich, exhaust smells like unburnt gas. I recently repaired an exhaust leak between bank 1 sensors front and rear, no change. oil smells strongly of gasoline. I was shocked just now when I touched the top of the coilpack, I'll spray some water on it tonight and see what I can see.

 

[2000StreetRod]

normally DTCs when misfire

The PCM computes the power pulse for each cylinder firing and recognizes when it is relatively low and reports a diagnostic trouble code (DTC). Since you have no misfire codes the low power must be fairly uniform for all cylinders. I suggest performing a compression test if one has not been already done. Make sure the throttle plate is held wide open when performing the test.

If the engine is running rich then the PCM should detect that and adjust the fuel trims to achieve the optimum air/fuel ratio. When the fuel trims reach their limits then the PCM should report a DTC. Since you have no rich codes the PCM must "think" the fuel mixture needs to be rich. Rich mixtures are needed when the engine is cold. If the engine coolant temperature (ECT) sensor is defective the PCM will "think" the engine is cold when it isn't. The easiest way to test the ECT sensor is to hook up a scanner to the OBD port and monitor the engine coolant temperature. The scanner would also allow you to monitor the fuel trims.

Is the intake system stock or have modications been performed?

What were the fuel pressures at idle and mid range? A leaking diaphragm in the fuel pressure regulator could result in high fuel pressure at idle and a rich mixture.

 

[NintendoKD]

The PCM computes the power pulse for each cylinder firing and recognizes when it is relatively low and reports a diagnostic trouble code (DTC). Since you have no misfire codes the low power must be fairly uniform for all cylinders. I suggest performing a compression test if one has not been already done. Make sure the throttle plate is held wide open when performing the test.

If the engine is running rich then the PCM should detect that and adjust the fuel trims to achieve the optimum air/fuel ratio. When the fuel trims reach their limits then the PCM should report a DTC. Since you have no rich codes the PCM must "think" the fuel mixture needs to be rich. Rich mixtures are needed when the engine is cold. If the engine coolant temperature (ECT) sensor is defective the PCM will "think" the engine is cold when it isn't. The easiest way to test the ECT sensor is to hook up a scanner to the OBD port and monitor the engine coolant temperature. The scanner would also allow you to monitor the fuel trims.

Is the intake system stock or have modications been performed?

What were the fuel pressures at idle and mid range? A leaking diaphragm in the fuel pressure regulator could result in high fuel pressure at idle and a rich mixture.

First of all, thank you for your post.
I'll be sure to check the ect sensor, you could be right. I will also do a compression test when I get a chance.
I do not have a scanner tool, just an el cheapo actron code scanner that tells me pend/codes and allows for clearing them, it will not show specific codes aka: ford break in codes vehicle disabled etc. Stock intake, all stock original, I re-ran a lot of vacuum lines, the hard plastic ones broke out here in the socal desert heat/dry air. I'll see what I can find out for you.

the fpr is good "not that it could be replaced anyway, part doesn't exist in heaven or hell" the diaphragm is good, holds vacuum well and does it's job. I believe right around 32psi and doesn't really drop even when revved, have no idea under load. I hooked a cheap air pressure tester "with the watch face" to the schrader valve on the fuel rail. I recently had to do a fuel line repair, PO did a number on the fuel line trying to cut the fuel filter out it appears.

 

[2000StreetRod]

fuel pressure

32 psi at idle is probably OK - certainly not excessive. The fuel pressure at idle should increase about 10 psi when the vacuum line to the fuel pressure regulator is disconnected.

 

[Flash]

Temperature sensor?

 

[NintendoKD]

inductive gun

I hooked up the timing gun to verify some things. All cyl misfire regardless of temp. except one. center drivers side cyl is the only one that fires consistently. I have been working on other things so the explorer has been on the back burner, that, and I'm pissed that I have spent like 2k in parts to fix this thing and it still isn't running right. I don't want to waste more money on this piece, and I'm not looking forward to putting in that sensor due to it's troublesome location.
I should add that I appreciate all the help so far.

 

[NintendoKD]

what resistance should the cts read when warm? maybe I can spoof it also is there just one? I know on my buddies dodge, there are two, one is for the pcm and the other is for the instrument cluster.

 

[budwich]

get a meter and measure the resistance. what about the crank sensor? checked the connector? cam sensor? checked the connector?

 

[2000StreetRod]

cold engine symptoms?

There are two engine temperature sensors. One drives the temperature gauge in the instrument cluster. It can totally fail and have no effect on how the engine runs. The other is the engine coolant temperature (ECT) sensor that the PCM relies on. If the engine runs fine when actually cold but rich when warm that increases the possibility of a defective ECT sensor. The ECT sensor is a thermistor that decreases in resistance as the temperature increases. Replacing it with a fixed resistor would make your air/fuel ratio incorrect for all engine temperatures except one. You can check the resistance by disconnecting the PCM connector and measuring the resistance across the two wires that go to the PCM. On my 2000 Sport the connections are Pin 38 (LG/RD) for ECT sensor input and Pin 91 (GY/RD) for Signal return.
BrooklynBay has a chart posted in his useful threads:
(25) Ford engine coolant temperature sensor (ECT) resistance chart.
For 50 deg F, R = 58.75 Komhs. For 86F, R = 24.27 Kohms. For 122F, R = 10.97 Kohms.

 

[Flash]

I don't want to waste more money on this piece, and I'm not looking forward to putting in that sensor due to it's troublesome location.

I know what you mean, I'm having a hell of a time diagnosing a spluttering condition on my Mondeo (Contour).

 

[NintendoKD]

the duratec, thats a good motor, never had an ounce of problems with it till I had to replace the alternator, then I wanted ill will against the engineer and anyone close to him. seems the best motors that ford has aren't theirs. where is the sensor located? is it in the same location at the t-stat housing, like I think it is "better not be" I have the autojunk part number as SU2103 is this the right one, or is it the instrument sender?

 

[NintendoKD]

the cam and crank sensors would cause all to misfire or not fire at all, but not just 5, and the other one is perfect, if its bad the symptom would be seen in all cyl. not just 5......right? connectors look good, cleaned the sensors too.

 

[budwich]

maybe.... but I am not sure that the method that you are using to check firing (induction timing gun) is totally valid... I do believe the system uses a "waste spark" which means you are most likely to get a "flash" all over the place. The sensors were just thoughts, not mentioned in your "list" and others have seen firing issues with poor connectors / bad / dirty sensors.